1. Field of the Invention
The present invention relates to information delivery and distribution, and more particularly, to a time division multiple access over broadband modulation method and apparatus that provides subscribers with allocated, unshared and deterministic bandwidth for upstream communications.
2. Description of Related Art
The demand for broadband content by business and residential subscribers is continually increasing. Broadband content includes multiple types of entertainment programming, communications and data, such as, broadcast television channels, video-on-demand, streaming video, multimedia data, Internet access, packet telephony, etc. To meet the increasing demand, it is typically necessary to increase bandwidth to each subscriber and to improve quality of service. Current delivery technologies include several variations of DSL (digital subscriber line) technology, such as ADSL (asymmetrical DSL) and the like, which uses telephony technology; cable modem systems using television technology and HFC (hybrid fiber coax) distribution networks; and 2-way wireless local loop (WLL) networks, including 2-way satellite services. However, existing technology for providing broadband content is becoming increasingly inadequate to meet the demand.
DSL technology is a method of delivering data over a twisted pair of copper wires or twisted pair cables, and typically uses public switched telephone networks (PSTN). There are several major problems with provisioning video services over the existing PSTN and twisted pair cables (network plant). For example, the existing network plant is not uniform and most of the plant is old with poor copper conditions that cause signal loss and line noise. In fact, ADSL cannot be provisioned for a large portion of the population over the existing plant because of significant distances to the closest DSL Access Multiplexor (DSLAM) and poor conditions of the existing plants. In addition, ADSL currently has a limited downstream bandwidth, and inherently provides a very limited return bandwidth. ADSL is not adequate for many types of content originating at a subscriber location, such as video conferencing and the like because of its bandwidth limitations and characteristics.
Cable modem systems for the delivery of data services using Data-Over-Cable Service Interface Specifications (DOCSIS) utilize the television broadcast spectrum and television technology to broadcast so-called broadband data to subscribers. One problem with delivery of broadband data using existing HFC networks is the limitation on available delivery spectrum. Television data delivery systems have been established to deliver data to subscribers over a television broadcast spectrum extending from approximately 15 Megahertz (MHz) to approximately 860 MHz. Delivery of analog television downstream to the subscriber occupies the spectrum between approximately 54 MHz to 550 MHz, which leaves a relatively small range of spectrum for the delivery of digital information over HFC cable modem systems. A diplex filter separating the downstream from the upstream is located within the frequency range of approximately 42 to 54 MHz in an extended sub-split frequency plan, which is common for consumer-based HFC systems. Therefore, the two effective delivery frequency ranges using typical consumer-based HFC systems are those between approximately 15-42 MHz (upstream) and those between approximately 550-860 MHz (downstream).
DOCSIS is a standard that specifies a methodology for delivering data services over an HFC plant. DOCSIS defines a Cable Modem Termination System (CMTS), which is an entity used to deliver data services over an HFC network from a central distribution point. These systems employ a shared frequency channel to broadcast all data to every downstream subscriber. The shared channel is generally 6 MHz wide providing a total data bandwidth of approximately 27-38 megabits per second (Mbps) for digital information. The channel, however, is shared among many subscribers, so that the data rate varies dramatically depending upon the time of use and the number of subscribers simultaneously logged on. The quality of service is particularly low during popular usage time periods. Moreover, conventional systems typically distribute the shared channel among at least four (4) separate nodes, each serving approximately 500 subscribers or more, so that resulting downstream data rate is often relatively low. The upstream shared channel is usually smaller, such as 3.2 MHz or less, and a “poll and grant” system is employed to identify data for upstream transmission. The resulting upstream performance is often no better (and sometimes less) than a standard 56 Kbps modem.